Vanadium alloys



United States Patent VANADIUM ALLOYS Karl F. Smith, Downers Grove, andRay J. Van Thyne,

Oak Lawn, Ill., assignors to the United States of America as representedby the United States Atomic Energy Commission No Drawing. Originalapplication November 8, 1957, Serial No. 695,470, now Patent. No.2,863,818, dated December 9, 1958. Divided and this applicationMay 29,1958, Serial. No. 751,582

Claims. (Cl. 75-134) This invention deals with new ternary alloys and inparticular with vanadium-base alloys and fuel elements jacketed withthese alloys.

Uranium fuel elements for sodium-cooled fastneutronic reactors, such asthey are described, for instance, in copending application, Serial No.437,017, filed by Walter H. Zinn on June 15, 1954, now Patent No.2,841,545, issued July 1, 1958, grow under the effect of radiation whichcauses jamming of the fuel elements; operation of such reactors istherefore hazardous. It has been tried to enclose the. fuel elements ofuranium metal, which is: to include elemental uranium anduranium-containing alloy s, with a jacket or can thathas. a. highstrength so that the fuel elements are restrained from expanding.

Zirconium and stainless steel have been used for this purpose, and. someimprovement, was obtained with the jackets made ofthese metals. However;there are certain disadvantages. in, connection, with the jackets usedheretofore. For instance, the iron of the stainless steel forms alow-melting (about 725 C.) eutectic with the uranium metal of the corewhich means destruction of the fuel element. Zirconium and the zirconiumalloys, primarily the zirconium alloy containing from 1 to 2.5 percenttin and up to 0.2 percent of iron, chromium, and nickel, do not showthis drawback, but they are not strong enough at elevated temperaturesto prevent the fuel element from growing. Other metals tested did notshow a sufficiently good heat conductivity which is a vital factor forsatisfactory operativeness of the reactor. Of the two metals usedheretofore stainless steel was the preferred material for uranium fuelelement jackets.

It is an object of this invention to provide an alloy suitable forjacketing uranium fuel elements which does not have the disadvantagesset forth above.

It is also an object of this invention to provide an alloy for jacketinguranium fuel elements which is superior to stainless steel.

It is an object of this invention to provide an alloy for jacketinguranium fuel elements which does not form a comparatively low-meltingeutectic with uranium.

It is another object of this invention to provide an alloy for jacketinguranium fuel elements which has a sufficiently high mechanical strengthand good creep resistance at elevated temperatures so that the uraniumcore is restrained from growing.

It is still another object of this invention to provide an alloy forjacketing uranium fuel elements which has a good thermal conductivity.

It is furthermore an object of this invention to provide an alloy forjacketing uranium fuel elements which has a low neutron-capture crosssection.

It is another object of this invention to provide an alloy for jacketinguranium fuel elements which has good corrosion resistance to practicallyoxygen-free sodium.

Finally, it is also an object of this invention to provide an alloy forjacketing uranium fuel elements that can be fabricated and welded.

Patented May 12, 1958 It was found that ternary vanadium alloycontaining from 2.5 to 15 percent by weight of titanium. and from 0.5 to10 percent by weight of niobium have the characteristics required andset forth above. The alloyscontaining about 10 percent of titanium andfrom 1 to 3 percent of niobium were the preferred compositions, and thealloy containing 10 percent of titanium and 3 percent of niobium yieldedthe most satisfactory results.

Vanadium forms a eutectic with uranium which melts at 1040 C. Whenimmersed in sodium that contains some oxygen (the sodium in fastreactors usually has a negligibly low oxygen content, though) vanadiumforms lower comparatively stable oxides, such as V0 and V 0 which formabarrier film on the surface and protect the vanadium or alloy againstfurther corrosion at elevated temperatures. I Nonalloyed vanadium metalwas first examined for the prime purpose of this invention, but it wasfound not to be superior, as to mechanical strength, to stainless steel347 (17 to 19 percent of chromium, 9 to 12 percent of nickel, up to 0.08percent of carbon and niobium in a quantity tenfold of that of carbon),the steel heretofore preferred for jacketing uranium fuel elements forfast neutronic reactors.

The alloys of this. invention can be prepared by any method known tothose skilledin the. art. The inventors preferred melting in an arcfurnace. The ingots obtained were heated to about 1350 C. and pressand.hammerforged to /2-inchand/or Vi-inch-diameter bars. The bars were thenground to size on a belt centerless grinder that had a belt 4 inches x54 inches anda grit size of 36,; the grinding material was aluminumoxide. All bars. were tested as to tensile strength at room temperatureand at 650 C; at a crosshe'ad speedjof 0.05"/ min. after they had beenannealed "at 6'5 0 C. for two days and water-quenched. Similarexperiments were carried out at 800 C., the annealing conditions in thatinstance having been 800 C. for 24 hours followed by waterquenching. Theresults of these tests together with the values obtained for yieldstrength, elongation and reduction of area are combined in the tablebelow, and the corresponding data for stainless steel and zirconium areadded for the sake of comparison. (Whenever heating of the alloys wascarried out, it was done in an inert atmosphere of helium or argon gas.)

ice

Tensile Yield Elonga- Reduc- Alloy Strength, Strength, tion, tion ofp.s.i. psi. Percent Area;

Percent V-10 Ti-l Nb 84, 600 63, 200 11 20 V10 Ti-3 Nb 97, 600 64, 50022 3B V-lO 'Ii-1 Nb 80, 400 58,000 15 41 V10 1i3 Nb 86,000 64, 000 21 48Stainless Steel 347. 51, 200 41, 000 46 71 Zirconium 15, 200 5, 000 3060 Zr-alloy 1.4% Sn, 0.2 Fe,

V10 'Ii-l Nb 55, 200 41, 600 13 33 Stainless Steel 347 23, 000

I at 480 C. I Not determined.

It is obvious from this table that tensile and yield strengths of thevanadium-titanium-niobium alloys are much superior to those of stainlesssteel and zirconium v 3 metals at elevated temperature and that theductility of these new alloys is lower, as is obvious from the data forelongation and reduction o'farea; however, the ductility isstillsufficient to make the alloys suitable and workable for the purposeof this invention.

The vanadium-l percent Ti-l percent Nb ternary alloy was also examinedas to stress rupture strength by applying different loads anddetermining the number of hours that were required to cause rupture.From a loadtime curve obtained from the results of these rupture teststhe strength bringing about exactly a 100-hour life was determined. Itwas found that at 650 C. the alloy Lw'ithstood a load of 62,000 lbs/sq.in. for 100 hours which compares with a strength of 27,000 p.s.i. forstainless steel 347 at the same temperature. At 800 C. the stressrupture strength, .for 100 hours, was 22,000 p.s.i.,

which compares witha stress .rupture strength of 9000 p.s.i, for 100hours with stainless steel 347 at.816 C. The alloys were furthermoretested for corrosion resistance in sodium that had a low oxygencontent,such as it is present in the sodium coolant of fast neutronic reactors.(The oxygen content in fast reactors has to be low to minimize transportcorrosion or in other words to prevent oxidation and pickup of the oxideformed from hot surfaces and deposition on cold surfaces.) The oxy- "gencorresponded to a content of less than 0.001 percent by weight of Na O.For the corrosion test, the alloys were immersed in the sodium at 700 C.for. twelve days, and the weight gain, which is an indication of thedegree Iof corrosion, was determined in each case. For the 10 percenttitanium-1 percent niobiumvand the 10 percent titanium-.3 percentniobium vanadium-base alloys the weights increased by 0.17 and 0.19percent, respectively.

Both alloys, that containing 1 percent and that containing'S percent ofnobium, .in addition to 10 percent of titanium, were found to besuperiorto zirconium as to heat conductivity and at least as good as. stainlesssteel 34']. The alloys 'were welded in an inert atmosphere,

e.g. of helium, using a tungsten electrode and an additional supply ofshielding gas to prevent contamination. The preferred conditions: were awelding rate of 14"/min., an electric current of amps. at 20 volts, anda total gas flow of 35 ft. /hr.; however, other conditions are alsosuitable.

The 10 percent Ti-l percent Nb ternary vanadiumbase alloy wascold-rolled (at room temperature, about 25 C.) satisfactorily to 95percent of reduction in thickness whereby a 2.5-mil thick sheet wasobtained.

While the invention has been described primarily in connection withjackets for fuel elements, it is understood that the alloys can be usedfor any purpose where one or several of the properties of the alloys ofthis invention are of importance, for instance, they can-be used asconstruction material of aircraft engines.

This is a divisiorr of copending application Serial No. 695,470, filedon November 8, 1957, now Patent No.

' 2,863,818, issued December 9, 1958.

It is also understood that the invention is susceptible to variousmodifications and changes, and that it is to be limited only by thescope of the appended claims.

. What is claimed is:

1. A ternary alloy containing from 2.5 to 15 percent by weight oftitanium, from 0.5 to 10 percent of niobium and from to 96.5 percent ofvanadium.

2. The alloy of claim 1 in which the titanium content ranges from 5 to10 percent and the niobium content from 1 to 3 percent. 3. The" alloy ofclaim 2 in which the titanium content is10percent.' W

4. An alloy. containing 10 percent of titanium, 3 percent of niobium,and 87 percent of vanadium.

,5. An alloy containing 10 percent of titanium, 1 percentot niobium, and89 percent of vanadium.

No references cited.

1. A TERNARY ALLOY CONTAINING FROM 2.5 TO 15 PERCENT BY WEIGHT OFTITANIUM, FROM 0.5 TO 10 PERCENT OF NIOBIUM AND FROM 80 TO 96.5 PERCENTOF VANADIUM.